A printer apparatus for outputting a receipt or the like is widely used for various purposes such as a cashier terminal of a shop or an ATM (Automated Teller Machine) or a cash dispenser of a bank. For example, a printer apparatus outputs a receipt by printing characters or the like on a recording paper (e.g., heat sensitive paper) with a thermal head while conveying the recording paper.
When using the printer apparatus, characters or the like are printed on the recording paper by providing the recording paper between the thermal head and a platen roller. The platen roller is detachably attached to the printer apparatus, so that the recording paper can be easily provided between the thermal head and the platen roller.
Accordingly, the recording paper is sandwiched between the thermal head and the platen roller by pressing the thermal head toward a side in which the platen roller is provided. In this state where the recording paper is sandwiched between the thermal head and the platen roller, printing by the thermal head is performed.
Thus, typically, a biasing member (e.g., coil spring) is provided behind the thermal head. One end of the coil spring or the like contacts the thermal head whereas the other end of the coil spring or the like contacts a rear surface support plate. Thereby, a recovering force of the coil spring or the like causes pressure to be exerted to the thermal head in the direction toward the platen roller via the rear surface support plate.
Patent Document 2 discloses a lock arm that supports a bearing of a platen roller in which a position of the platen roller is defined by using a biasing force of a pressure spring exerting pressure to a thermal head. Patent Document 4 discloses a configuration that includes a first spring provided between a lock arm and a thermal head for biasing a platen roller in a direction toward the thermal head, and a second spring provided between the thermal head and a frame body for biasing the thermal head in a direction to contact the platen roller.    [Patent Document 1]: Japanese Patent No. 3734753    [Patent Document 2]: Japanese Patent No. 3599595    [Patent Document 3]: Japanese Laid-Open Patent Publication No. 2000-318260    [Patent Document 4]: Japanese Laid-Open Patent No. 2008-68551    [Patent Document 5]: Japanese Laid-Open Patent No. 2000-94767
Typically, in a case of a thermal printer that prints characters or the like on a recording medium by using a thermal head, a platen roller is retained by a lock arm by way of, for example, a platen bearing formed of a mold resin or the like. The thermal printer that is used for various purposes may be accidentally dropped or applied with an unexpected amount of force when the thermal printer is being used. In this case, the platen bearing or other members of the platen roller may be damaged (malfunction) and become unusable if the platen roller cannot disengage from the thermal printer.
Specifically, in a case of, for example, a thermal printer that has a lock arm formed in its disengaging direction (removing direction) in a manner covering a large portion of the platen bearing or the like of the platen roller, the platen roller may not easily disengage from the thermal printer even if force is exerted to the thermal printer when the thermal printer is dropped. Thus, if the platen roller cannot disengage from the thermal printer, the platen bearing or the like could be damaged by the impact caused when, for example, the thermal printer is dropped. As a result, the thermal printer can no longer be used.